Distributed Fluid Velocity Sensor and Associated Method

ABSTRACT

Device and method for performing distributed fluid velocity measurement. An elongate device comprising along its length, a heated core ( 200 ), at least one outer layer ( 240 ) around the core, the outside surface of the outer layer ( 240 ) defining an outside surface of the device, and a distributed temperature sensor ( 230 ) located between the heated core ( 200 ) and the outside surface of the device. The method immerses the device in one or more fluids along its length, measures the ambient temperature of the fluids at points along it&#39;s length, heats the heated core ( 200 ) for a predetermined heating period and measures the temperature again at the same points. Using pre-installed knowledge the device can obtain distributed and/or point fluid velocity measurements.

The oil and gas industry is very dependent on well bore measuring techniques to provide information about what is actually happening deep in a well bore. Many surveys are done before oil or gas is produced, including seismic and rock porosity, water content and micro seismic. However, there are few methods of obtaining data which gives a broad measurement of the behaviour of the well over its whole length.

Point pressure and temperature sensors have been in commonplace use since the 1940's and production logging tools are also now in common use. It is quite common in the oil and gas industry to run optical distributed temperature sensing systems into oil wells to measure the temperature profile over the complete length of the well bore.

The point sensors only provide indications of what is happening at the position of the sensor. Logging tools measure the complete well bore, but not in real time and they can only be run periodically. Logging tools are also difficult to run when there are pumps in the well bore. Distributed temperature measurement is limited by the fact that, while the temperature profile can be interpreted to give information about other behaviour in the well bore, the temperature information in its raw state is not immediately useful in terms of determining the fluid produced (or injected), or more importantly the fluid flow rates.

The oil and gas industry is under pressure to achieve greater efficiency and increase production rates, all of which requires more understanding of reservoir storage and production behaviour. This has created a need for more 2-dimensional and 3-dimensional measurements of reservoir behaviour.

It is therefore an aim of the present invention to address one or more of the above issues.

In a first aspect of the invention there is provided an elongate device for performing distributed fluid velocity measurement, comprising along its length:

-   -   a heated core,     -   at least one outer layer around said core, its outside surface         defining an outside surface of the device, and     -   a distributed temperature sensor;         wherein said distributed temperature sensor is located between         the heated core and the outside surface of the device.

Using such a device it is possible to measure heat loss from the core to its environment from, for example, the temperatures before and after a period of heating using the heated core.

Said distributed temperature sensor may comprise a fibre-optic distributed temperature sensor. Said distributed temperature sensor may be coiled helically around said heated core. Said distributed temperature sensor may be embedded within an insulation layer around said core. There may be at least one intervening layer between said insulation layer having said distributed temperature sensor embedded therein and said heated core. The insulation layer having the distributed temperature sensor embedded therein may be said outer layer of the device, or else said outer layer may be additional to this insulation layer comprising the distributed temperature sensor.

Said device may comprise a cable.

Said heated core may comprise a resistance wire.

Said device may further comprise control and processing means for controlling the heating of the heated core and processing the results obtained from the distributed temperature sensor.

Said device may further comprise a distributed fluid identification device for identifying a fluid that said device is immersed in at each of a plurality of measurement points of said device.

Said device may further comprise a distributed fluid identification device for identifying a fluid that said device is immersed in continuously over the length of said device.

Said device may be operable to: measure the ambient temperature of a fluid that it is immersed in at a plurality of measurement points along its length; turn on the heated core for a predetermined heating period, and take temperature measurements again at the same measurement points. Said device may be further operable to use obtained or pre-installed knowledge of the appropriate fluid characteristics so as to process said results obtained from the distributed temperature sensor to obtain distributed and/or point fluid velocity measurements for the fluid passing over the surface of said device. Said device may be further operable to determine real-time distributed and/or point fluid flow information from said distributed and/or point fluid velocity measurements. Said device may be further operable to use obtained or pre-installed knowledge of a number of fluid characteristics to identify which of said number of fluids it is immersed in at any one measurement point directly from the measured temperature at said particular measurement point after said predetermined heating period.

Said device may comprise a semi rigid construction to allow injection into well bores; for example said device may comprise a rigid element such as carbon fibre along its length.

in a second aspect of the invention there is provided a plurality of said devices operable to provide a 3-dimensional array of measurement points within a fluid in which said plurality of devices is immersed.

In a further aspect of the invention there is provided a method of performing distributed cooling measurements using the device, or plurality thereof, according to either of the above aspects of the invention, comprising the steps of:

immersing said device in one or more fluids along its length; measuring the ambient temperature of said fluid or fluids at a plurality of measurement points along its length; turning on the heated core for a predetermined heating period; and measuring the temperature again at the same measurement points.

Said method may be further comprise using obtained or pre-installed knowledge of the appropriate fluid characteristics so as to process said distributed cooling measurements so as to obtain distributed and/or point fluid velocity measurements for the fluid or fluids passing over the surface of said device. Said method may comprise the further step of determining the real-time distributed and/or point fluid flow information from said distributed and/or point fluid velocity measurements.

Said method may comprise obtaining information to identify said fluid or fluids at the same time as performing said distributed cooling measurements.

Said method may comprise using obtained or pre-installed knowledge of a number of fluid characteristics to identify which of said number of fluids it is immersed in at any one measurement point directly from the measured temperature at said measurement point after said predetermined heating.

Said method may comprise deploying said device in a well bore, in a pipeline where it can be used to detect and/or locate leaks and/or branches, or in a fluid storage facility such as a tank, reservoir, separator etc. in the latter case, multiple devices may be installed as per the second aspect of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example only, by reference to the accompanying drawings, in which:

FIG. 1 depicts a cable based sensor array according to an embodiment of the invention;

FIGS. 2 a and 2 b show the cable based sensor of FIG. 1 in cross-section and isometric views respectively;

FIG. 3 a device comprising the cable based sensor of FIG. 1 in combination with a distributed fluid identification sensor;

FIGS. 4 a-4 c show three examples of how a cable based sensor array may be installed in a well bore;

FIG. 5 shows two examples of how a cable based sensor array may be installed in a pipeline; and

FIG. 6 shows two examples of how such a cable based sensor array, or plurality thereof, may be installed in a tank, reservoir or similar.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 depicts a cable based sensor array for use in oil and gas wells, or any deep well bore, or pipe line. The system comprises a cable 110 which is deployed into the well bare 120 in reservoir 130 and a surface electronics control and processing unit 135, which processes and records the information. The surface electronics control and processing unit 135 shown here comprises a heater control 140, a fibre optic distributed temperature sensor (DTS) measurement apparatus 150 and a central data logger and data handling unit 160. The well bore 120 in this example contains a water layer 170, an oil layer 180 and a gas layer 190. The sensor array can be many kilometers long, and be able to determine distributed fluid flow rates along its full length.

The cable based sensor array 110 is shown in greater detail in FIGS. 2 a and 2. It comprises a heated wire core 200 with a glass fibre sheath 210. Around this is a high temperature resistant sheath 220. Spiralled around the outside of sheath 220, and embedded within outer layer 240 is a fibre optic temperature sensor array 230, such as an ⅛ inch OD tube encapsulated fibre optic temperature probe. The cable based sensor array 110 is encapsulated by an outer shell 250.

The heated core 200 can comprise any heat source means (including a heated fluid), but in a main embodiment comprises a current carrying wire heated by resistance heating. Using a resistance wire simplifies temperature control compared to other heating methods, and also provides for a substantially uniform heat rise above ambient along its length.

The fibre optic sensor array 230 may be any of the types known in the art The use of intrinsic fibre optic sensors to provide distributed temperature sensing over very large distances is well known. For example, temperature can be measured by using a fibre that has evanescent loss that varies with temperature, or by analyzing the Raman scattering of the optical fibre. The fibre optic sensor array 230 is located between the heated wire core 200 and the outside surface of the device, along the sensing length of the device.

The cable based sensor array 110 operates by measuring the cooling effect resultant from the fluid or gas flowing over the surface of the cable. It does this, in one operational embodiment, by first measuring the ambient well bore temperature at each optical measurement point being considered, followed by switching the heated core on for a predetermined heating period, and then taking temperature measurements again at the same optical measurement points. The temperature rise caused by the heated core at each measurement point is dependent on the thermal cooling of the walls of the cable at that point, which in turn is dependent on, and therefore allows the measurement of, the fluid velocity characteristics around the cable surface at that point. The principle of fluid velocity measurement using cooling of a heated object is well proven and documented uses date back to 1904.

Of course, to obtain the of fluid velocity measurement from the cooling information, the nature of the fluids must be known since the cooling resultant from each fluid is different. FIG. 3 shows a further embodiment comprising a combined cable based sensor array 110 with a distributed fluid type sensor array 300 to obtain a very powerful fluid analysis and measurement system. Both arrays have surface control and processing units 135, 310 (which may be comprised within the same unit). This combined array therefore can be used to measure the cable surface cooling and determine the fluid characteristics at all points in the array, and therefore determine the fluid velocity at any point in the sensor array. From this sensor surface velocity information the processing units can calculate fluid flow rates in real time.

The cable based sensor array 110 can also be used without any further sensors to determine the type of fluid present, provided that sufficient information on the thermal conductive character of the fluid present is known. If so, then the absolute temperature of the surface at the end of the predetermined heating period will be indicative of the nature of the fluid flowing. This is easily appreciated by considering the fact that gases typically will cool the surface of the sensor much less than liquids will. By using set values and having pre-observed the temperature rises created by different flowing fluids, the type of fluid can be determined directly from the final temperature reading.

FIGS. 4 a-4 c show three examples of how such a cable based sensor array may be installed in a well bore. FIG. 4 a shows the cable based sensor array 110 installed permanently in the well bore 120, strapped to a tubing string 400. FIG. 4 b shows an alternative whereby the cable based sensor array 110 is lowered into a well through a lubricator (not shown) and hung off the well head freely suspended. At the bottom end may be weights and/or an anchor 410. By way of another example the cable based sensor array 110 may be deployed in a similar way to a logging tool using a spooler 420 and injector 430, and left in the well bore as shown in FIG. 4 c in such an alternative, the cable system 110 could also be built as a semi rigid cable to enable it to be pushed into well bores. For example, the cable construction may be altered to include a rigid element such as carbon fibre.

The cable based sensor array 110 has many applications other than the measurement of fluid and gas flow characteristics over the length of an oil or gas well and the providing of information on the fluid being produced in each rock formation as already described.

FIG. 5 depicts an operational embodiment where the cable based sensor array 110 is deployed in pipelines 500 to determine the position of leaks 510, injection points 520 or outlet branches 530. In smaller forms it could be deployed across the diameter of a pipe to measure in real time the flow profile in a pipe.

FIG. 6 depicts a further operational embodiment where the cable based sensor array 110 is deployed in a storage tank, separator or even reservoir 600 or any other large body of fluid 610. In the first example only one cable based sensor array 110 is being used, which could take any configuration, whether L-shaped, as shown, or vertical, horizontal or any other 2- or 3-dimensional configuration. The second example depicts a plurality of cable based sensor arrays 110 (one row of sensor arrays 110 is shown, but there may be more) which can be used to create a 3-dimensional model of the flowing behaviour of the complete reservoir or tank. Again, each array 110 could take another configuration. Also, while each sensor array 110 is shown with a dedicated control and processing unit 135, the system may instead have a single control and processing unit for all the arrays 110, or a subset thereof.

While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. For example, features of the invention, such as those for processing, may take the form of a computer program containing one or more sequences of machine-readable instructions describing a method as disclosed above, or a data storage medium (e.g. semiconductor memory, magnetic or optical disk) having such a computer program stored therein.

The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below. 

1. An elongate device for performing distributed fluid velocity measurement, comprising along its length: a heated core, at least one outer layer around said core, the outside surface of said at least one outer layer defining an outside surface of the device, and a distributed temperature sensor; wherein said distributed temperature sensor is located between the heated core and the outside surface of the device.
 2. A device as claimed in claim 1 wherein said distributed temperature sensor comprises a fibre-optic distributed temperature sensor.
 3. A device as claimed in claim 1 wherein said distributed temperature sensor is coiled helically around said heated core.
 4. A device as claimed in claim 1 wherein said distributed temperature sensor is embedded within an insulation layer around said heated core.
 5. A device as claimed in claim 4 wherein there is at least one intervening layer between said insulation layer having said distributed temperature sensor embedded therein and said heated core.
 6. A device as claimed in claim 1 wherein said device comprises a cable.
 7. A device as claimed in claim 1 wherein said heated core comprises a resistance wire.
 8. A device as claimed in claim 1 comprising control and processing means for controlling the heating of the heated core and processing the results obtained from the distributed temperature sensor.
 9. A device as claimed in claim 1 comprising a distributed fluid identification device for identifying a fluid in which said device is immersed.
 10. (canceled)
 12. (canceled)
 13. (canceled)
 14. (canceled)
 15. (canceled)
 16. A device as claimed in claim 1 comprising a semi rigid construction to allow it to be injected into well bores.
 17. A device as claimed in claim 16 comprising a rigid element such as carbon fibre along its length.
 18. A plurality of devices as claimed in claim 1 being operable to provide a 3-dimensional array of measurement points within a fluid in which said plurality of devices is immersed.
 19. A method of performing distributed fluid velocity measurements using at least one elongate device comprising along its length: a heated core, at least one outer layer around said core, the outside surface of said at least one outer layer defining an outside surface of the device, and a distributed temperature sensor; wherein said distributed temperature sensor is located between the heated core and the outside surface of the device; the method comprising the steps of: immersing said device(s) in one or more fluids along its length; measuring the ambient temperature of said fluid or fluids at a plurality of measurement points along its length; turning on the heated core for a predetermined heating period: and measuring the temperature again at the same measurement points.
 20. A method as claimed in claim 19 further comprising the use of obtained or pre-installed knowledge of the appropriate fluid characteristics so as to process said distributed cooling measurements to obtain distributed and/or point fluid velocity measurements for the fluid or fluids passing over the surface of said device or devices.
 21. A method as claimed in claim 20 further comprising the step of determining the real-time distributed and/or point fluid flow information from said distributed and/or point fluid velocity measurements.
 22. A method as claimed in claim 20 further comprising said method comprises obtaining information to identify said fluid or fluids at the same time as performing said distributed cooling measurements.
 23. A method as claimed in claim 19 further comprising using obtained or pre-installed knowledge of a number of fluid characteristics to identify which of said number of fluids it is immersed in at any one measurement point directly from the measured temperature at said measurement point after said predetermined heating.
 24. A method as claimed in claim 19 comprising the initial step of deploying said device or devices in a well bore.
 25. A method as claimed in claim 19 comprising the initial step of deploying said device or devices in a pipeline so as to detect and/or locate leaks and/or branches, and/or to determine flow rates therein.
 26. A method as claimed in claim 19 comprising the initial step of deploying said device or devices in a fluid storage facility such as a tank, reservoir or separator. 